1. Field of the Invention
The invention relates to an inkjet pen and a pressure control device thereof; in particular, to an inkjet pen with a pressure control device that can properly actuate its bubble generator.
2. Description of the Related Art
Conventional ink-jet printing generally relies on the controlled delivery of ink droplets,from a reservoir of an inkjet pen to a print medium. Among the printing methods for delivering ink drops from the reservoir to the print head, drop-on-demand printing is known as a commonly used method. Drop-on-demand typically uses thermal bubble or piezoelectric pressure wave mechanisms. A thermal bubble type print head includes a thin film resistor heated to cause sudden vaporization of a small portion of ink. The rapid expansion of the ink vapor forces a small drop of ink through a print head nozzle. Although drop-on-demand printing is ideal for sending ink drops from a reservoir to the print head, some mechanism must be included to prevent ink leaking out from the print head when the print head is inactive. Such a mechanism usually builds a slight backpressure at the print head to prevent ink leakage from the pen when the print head is inactive. Herein, the term xe2x80x9cbackpressurexe2x80x9d represents the partial vacuum within the reservoir. Backpressure is defined in the positive sense so that an increase in backpressure means the degree of partial vacuum has increased.
When the backpressure is established at all times inside the reservoir, ink is prevented from permeating through the print head. However, the backpressure cannot be so high that the print head is unable to overcome the backpressure to eject ink drops. Furthermore, as ambient air pressure decreases, a correspondingly greater amount of backpressure is needed to keep ink from leaking. Accordingly, the backpressure within the inkjet pen has to be regulated whenever ambient pressure drops. Also the pressure within the pen is subjected to what may be termed xe2x80x9coperational effectsxe2x80x9d, as the depletion of ink from the reservoir increasing the backpressure of the reservoir. Without regulation of this backpressure increase, the inkjet pen will fail quickly because the backpressure is too high for the print head to overcome and eject ink drops.
Conventionally, the backpressure within the reservoir is controlled by mechanism referred to as accumulators. In general, an accumulator includes an elastomeric bag capable of moving between a minimum volume position and a maximum volume position in response to changes in the backpressure within the reservoir. For example, as ambient pressure drops so that backpressure within the reservoir decreases simultaneously, the accumulator will move to increase the volume of the reservoir to thereby increase the backpressure to a level sufficient to prevent ink leakage. Another example is depletion occurring during operation of the pen. In such a case, accumulators will move to decrease the volume of the reservoir to reduce the backpressure to a level within operating range, thereby permitting the print head to continue ejecting ink.
However, although accumulators such as elastomeric bags can automatically adjust the volume of the reservoir to keep the backpressure within the operating range, the extent to which elastomeric bags are capable of expanding is quite limited. Consequently, when ink level gradually drops from the print head, the bag may reach its maximum extent and therefore become incapable of any further adjustment of the volume of the reservoir. Hence, the backpressure within the reservoir may increase such that ink droplets are prevented from leaving the print head.
To resolve the aforementioned problems, some inkjet pens employ a device called a xe2x80x9cbubble generatorxe2x80x9d. The bubble generator has an orifice through which ambient air can enter the reservoir. The dimension of the orifice is such that ink is trapped within the orifice to seal off the reservoir by capillary effect. When ambient air pressure is high enough to overcome the liquid seal, air can bubble into the reservoir. Therefore, the backpressure within the reservoir can decrease and capillary effect will take over and re-establish the liquid seal again to prevent entrance of more air bubbles.
In general, bubble generators of inkjet pens must satisfy a few conditions. Firstly, the bubble generator must be able to precisely control backpressure. Secondly, the range of fluctuation of the backpressure within the reservoir must be as small as possible. In other words, as air bubbles enter the reservoir leading to a drop in backpressure, the bubble generator must be able to stop the entrance of bubbles soon enough that sufficient backpressure remains inside. Thirdly, the bubble generator must have self-wetting capability. The liquid seal must be able to prevent the entrance of bubbles even when most of the ink within the reservoir is used up, or alternately when the inkjet pen is tilted such that the bubble generator is no longer immersed in the ink.
FIG. 1 shows a conventional inkjet pen 100 according to U.S. Pat. No. 6,213,598. The inkjet pen 100 comprises a flat spring 21 welded to the bottom of an inkjet pen 100. The flat spring 21 presses a sphere 22 of a bubble generator 30. An expandable bag 23 is in contact with a pressure plate 25, and the pressure plate 25 is supported by a spring 24. The flat spring 21, the sphere 22, the expandable bag 23, the spring 24, and the pressure plate 25 constitute a pressure control device 20 of the inkjet pen 100.
As stated above, in the conventional inkjet pen 100, the bubble generator 30 is actuated by the pressure plate 25. The pressure plate 25 is moved by the expandable bag 23. However, the motion of the pressure plate 25 by the expandable bag 23 is difficult to control.
Specifically, the pressure plate 25 is provided with a certain area; however, the contact area between the pressure plate 25 and the expandable bag 23 is very limited. Thus, when the pressure plate 25 is moved by the expandable bag 23, the bubble generator 30 cannot be properly actuated by the lower portion of the pressure plate 25. That is, when the pressure plate 25 is moved by the expandable bag 23, the upper portion of the pressure may be moved first. As a result, the lower portion of the pressure plate 25 may not be moved, thereby failing to properly actuate the bubble generator 30.
In view of this, the invention provides an inkjet pen with a pressure control device that can properly actuate its bubble generator.
Accordingly, the invention provides an inkjet pen. The inkjet pen comprises a body, a bag, a pressure plate, an abutting member, and a rib. The body includes a bubble generator. The bag is disposed inside the body, and communicates with the external environment so as to expand inside the body. The pressure plate, disposed inside the body and located adjacent to the bag so as to move inside the body, includes a first portion arid a second portion. The first portion is located near the bubble generator. The abutting member is disposed in the body, and seals the bubble generator. The rib is disposed in the body and located near the second portion of the pressure plate. The second portion of the pressure plate is maintained at a predetermined position by the rib when the pressure plate is moved by the bag. Thus, the abutting member is properly moved by the first portion of the pressure plate when the pressure plate is moved by the bag.
In a preferred embodiment, the rib is disposed on the pressure plate.
It is understood that the rib may be integrally formed on the pressure plate.
In another preferred embodiment, the rib is integrally formed on the body.
In another preferred embodiment, the abutting member is a spring leaf.
In another preferred embodiment, the abutting member is disposed on the first portion of the pressure plate.
In another preferred embodiment, the inkjet pen further comprises an elastic member disposed in the body, adjacent to the pressure plate.
It is understood that the elastic member may be a spring.
In another preferred embodiment, the bubble generator comprises a sealing member disposed in the body in a moveable manner so as to seal the bubble generator.
It is understood that the sealing member may be a sphere.